Italian Prime Minister Giuseppe Conte, right, flanked by Deputy Prime Minister Matteo Salvini, addresses the Senate in Rome on Aug. 20. (Gregorio Borgia/AP)

IN POLITICS, nothing lasts forever. And in Italian politics, nothing lasts for more than a few months, or so it sometimes seems in that perennially fractious country. Skepticism is thus in order regarding the staying power of a new center-left coalition government that is emerging in Rome.

Still, the new coalition represents a potentially promising development. It would replace a 14-month-old left-right populist hybrid that had been increasingly dominated by rightist Matteo Salvini, who made a name for himself through relentless attacks on the European Union and a hostile attitude toward the migrants who cross the Mediterranean and toward the nongovernmental groups that help them. Mr. Salvini had proved both disruptive in his ostensibly subordinate role as deputy prime minister and increasingly popular. Riding his nationalist rhetoric to a first-place position in opinion polls, the leader of the League party precipitated the current crisis — in the apparent belief that he could win a general election after dissolving his coalition with the more left-leaning populist Five Star Movement. His most recent provocation was his refusal, as Italy’s interior minister, to allow a migrant ship carrying children to dock, although he eventually relented and agreed to let 27 minors disembark.

Mr. Salvini failed to anticipate that Five Star would pivot to a new parliamentary alliance with its previously hated rivals, the Democrats, the center-left remnants of Italy’s postwar political establishment. If the two parties can maintain their truce, their new majority’s term could last until 2023, relegating Mr. Salvini, his ambitions and his far-right ideology to the sidelines.

That happens only if the new government succeeds, which, in turn, hinges on the ability of the prime minister, Giuseppe Conte, to deliver sound government to a country that has known precious little of that in recent years. Mr. Conte served in the previous coalition, as a compromise between the populist factions, and his continuance was Five Star’s price for allying with the Democrats. Now elevated from political middleman to protagonist, Mr. Conte has already surprised on the upside by delivering a stirring speech in which he rebuked Mr. Salvini as “irresponsible.” He must follow that up by rejoining European talks on migration policy, which Mr. Salvini had snubbed, and by properly managing the country’s stagnant economy, starting with a draft budget due in October.

The European Union can make the job easier for Mr. Conte by adopting pro-growth reforms to its austere fiscal policies, and by carrying out a more rational and efficient distribution of migrants among E.U. members . The E.U. should do both, because a more prosperous Italy, confident it won’t have to deal with a migratory flow all by itself, would be an Italy more securely anchored in the E.U. Brussels and Rome should urgently seize the chance to work together; they may have the upper hand on Mr. Salvini for now, but he remains a potent force in Italian politics, waiting to exploit any mistake by Mr. Conte to mount his comeback.